Fuel cells can be used for generating electricity when being fed with fuel and oxygen, for example hydrogen and oxygen. However, a fuel cell can be also operated in a reversed manner. In this case a fuel cell can be fed with electricity for conducting an electrolysis process in order to generate for example oxygen and hydrogen out of water or water vapor. When using a fuel cell in this operation mode, a fuel cell can be used to exploit an over-generation of electricity and to produce high quality fuel. This fuel can be for example stored in a much easier way than the electricity may be stored. In particular, it is easier to store hydrogen than storing an equivalent electricity or electric energy. Further, it is possible to generate a high quality fuel for other purposes, like for example heating purposes. However, handling of hydrogen may generate additional problems, as a high pressure is required for compressing hydrogen in order to reduce the storing volume. Further, using hydrogen as fuel may cause serious safety issues, as hydrogen under particular circumstances may be highly explosive. Therefore, the hydrogen may be converted into methane by way of a methanation process. In this way, hydrogen may be converted methane, so that this methane can be fed to public fuel or gas grids. Such a process is described, for example, in the Korean patent application No. 10-0814156 or Korean patent application No. 10-1093674. U.S. 2004/0202914 describes a fuel cell arrangement having a reactor tube including a catalyst for a methanation process. The reactor tube is downstream the fuel cell and connected by conduits. A Heat exchanger by be arranged between the fuel cell and the reactor tube. DE 10 2011 088 613 describes a fuel cell having an internal actuator for controlling the fuel cell. EP 2 540 388 describes a method for operating a methanation reactor and a methanation reactor. Based on the above aspects, it may be of advantage to have a fuel cell arrangement having a higher efficiency over the prior art fuel cell arrangements.